Nail Bottle Demonstration in Slow Motion

Tom Kuntzleman | Fri, 02/21/2014 - 11:27

The nail bottle demonstration1 is one that many of us have conducted in our classes. To perform this demonstration, 2 – 3 mL of ethanol is placed into a plastic bottle that has two nails punctured into opposite sides of the bottle. After stoppering the bottle, a Tesla coil is touched to one of the nails. A spark jumps from one nail to the other, which initiates the combustion of vaporized ethanol inside the bottle:

I have seen this reaction performed many times, but never in slow motion like this! When I first observed this reaction in slow motion, I was amazed by the way that the initial reaction front seemed to proceed spherically outward, at least until the reaction front was impeded by the walls of the bottle. This observation made me wonder if the reaction started with a single molecular event. Upon further reflection, I noticed that the spherical reaction front in the nail bottle looked remarkably similar to the spherical shape flames take on in zero gravity. In the presence of gravity, flames rise because hot gases are more buoyant than surrounding cold air. In zero gravity, the hot gases in a flame expand, but don’t move upward because there is no buoyant force. Therefore, a flame is shaped like a tear drop in the presence of gravity but like a sphere in the absence of gravity.

So why does the initial flame in the nail bottle – which is certainly under the influence of gravity – proceed in a spherical manner? My guess is that the gases produced in the initial, most violent stage of the reaction expand so forcefully that the buoyant forces on these gases are negligible by comparison. In a sense, the initial flame front in the nail bottle simulates a flame in zero gravity!

The questions and observations I have when watching this video leads me to wonder what some of you might think after viewing this video. When you observe the nail bottle reaction in slow motion, what questions come to your mind? What observations have I have missed? Would you like to see this reaction filmed in a different way? Share your questions, comments and ideas with us!

Comments 3

I love these super slo-mo videos! Keep them coming, Tom! For me, these videos create more questions than provide answers, and this video is no exception. In addition to Tom's observations and questions I add my own. A lot is going on here that I could not see otherwise and leads me to ask...

What is going on with the second wave of combustion? Is additional ethanol vaporizing and burning after the initial vapor and is this ignited by a second spark?

What happened toward the end where it looks like something fell into or was sucked into the bottle and burned?

Perhaps the answers to these observations and questions lie in Tom's thinking about gravity and its influence on what we observe. It may be that these secondary observations occur because now gravity can exert its influence.

These videos provide wonderful opportunities to share with your students how a chemist would observe and think about those observations. Please share this video with your students, see what questions arise and encourage them to share in this forum.

The video does spark many questions. I am looking forward to sharing with my students. As Tom mentions, this is a demo that many of us already use. I can show the video after and ask my students to jot some notes about what they see and what questions they have. Sometimes it is difficult to get students to join in a discussion, but I think using the slow motion video will help excite them to participate.

Jon, I think what you are seeing at the end of the video is air rushing in after the hot air of the explosion rushes out (there is a vacuum created in the bottle for a moment). Is there something coming in and burning or is the additional oxygen that rushes in allowing for a little more combustion of alcohol?

I try to get my students to realize that thinking about concepts and engaging in these types of conversations helps us to understand the concepts even if we walk away with more unanswered questions than answered ones. That is science.

Since the reaction occurs in the middle of the bottle, unaffected initally by the shape of the bottle, why wouldn't you expect the expansion to be the same in all directions? I expect that gravitational forces have very little to do with the shape of the flame in comparison to the force outward as a result of the inital combustion between the nails. You may notice that there is a distinctive aldehyde smell if you waft the air from the bottle soon after the reaction stops. The combustion quickly exhausts the oxygen, and the aldehyde forms as a result.(Incomplete combustion)